Generation of humic and fulvic acid from Callovo-Oxfordian clay under high alkaline conditions

Low-carbon-containing clay from four different depths (447 to 516 m) of the Meuse Haute Marne (MHM) site is kept in contact with alkaline solution simulating conditions expected from cement dissolution in the near-field of a nuclear waste repository. Original organic material in the clay consists mainly of aliphatic hydrophobic compounds basically without oxygen-containing functional groups. After contact with ‘solid young fluid’ (mimicking cement dissolution, initial pH 13.22) for approximately one and a half years, high concentrations of hydrophilic organic matter are found (243–355 mg DOC/L). Characterization by solubility behavior, UV/Vis absorption, IR and fluorescence properties show that the dissolved hydrophilic organic matter has the characteristic features of humic and fulvic acids. Estimation of humic and fulvic acid content via UV/Vis spectroscopy results in 97.5 (±9.7)% of DOC being humic and fulvic acid. The results indicate that this could be an important source of complexing mobile organic matter influencing the mobility of radionuclides in a nuclear waste repository under consideration for this site. Investigations were conducted under oxic conditions representing the situation in the excavation disturbed zone (EDZ) of an underground facility. Sample amounts were very small and thus some characterization results are partly of preliminary character.